1-Diazo-2-propene

[2032-04-4]  · C3H4N2  · 1-Diazo-2-propene  · (MW 68.08)

(reagent for the cyclopropanation of alkenes)

Alternate Name: vinyldiazomethane.

Solubility: vinyldiazomethane is most commonly prepared and used as a solution in ether or THF, or as an alcoholic solution in either of those solvents.

Analysis of Reagent Purity: the amount of active diazo compound contained in a solution has been determined by measuring the volume of nitrogen evolved upon reaction of an aliquot of the diazo compound with an excess of p-nitrobenzoic acid in THF.3

Preparative Methods: the reagent is most commonly prepared by the action of base on various N-allyl-N-nitroso derivatives. Thus ethyl-N-allyl-N-nitrosocarbamate has been used,1 as has N-allyl-N-nitrosourea.2 The reagent is light sensitive and should therefore be shielded from light during its preparation. It undergoes isomerization to pyrazole at rt1c and is therefore prepared immediately prior to use, and not usually stored for any length of time. Furthermore, it is potentially explosive and for this reason the chemist is advised to follow carefully the exact procedure given for a particular preparation and perform all operations behind a blast shield in a well ventilated fume hood.

Handling, Storage, and Precautions: in addition to the previously mentioned explosion hazard which this reagent presents, there are health related hazards that must also be considered. Diazo compounds, as a class, are toxic and irritating and can be sensitizers. They must be used in a well ventilated fume hood and not come in contact with skin. For a description of the hazards associated with this class of compounds, see the handling and storage precautions listed for Diazomethane.

Cycloadditions.

Vinyldiazomethane is commonly used to prepare vinylcyclopropane derivatives from alkenes, either via transition metal-catalyzed cyclopropanation, or via an intermediate pyrazoline. In the case of the transition metal-catalyzed process, the product cyclopropane contains an alkene which can react further with the starting vinyldiazomethane. The procedure is therefore limited to alkenes which can be used in large excess, or which are substantially more reactive than the product alkene. Thus low boiling, electron-rich alkenes have been used in large excess with various copper(II) salts as the catalysts.3 Of the various copper salts examined, Copper(II) Trifluoromethanesulfonate, copper(II) trifluoroacetate, and Copper(II) Hexafluoroacetylacetonate were found to provide low to moderate yields (12-40%) of the desired cyclopropane from cyclohexene. Copper(I) iodide and copper(II) chloride, carbonate, and sulfate were found to be ineffective. The reaction is stereospecific, with cis- and trans-alkenes providing the corresponding cis- and trans-cyclopropanes, respectively (eqs 1 and 2).

Rhodium(II) complexes have also been examined as catalysts for cyclopropanation, and have been found to be more effective than copper salts.4 The reaction works well for enol ethers and dienol ethers, with cyclopropanation preferentially occurring at the alkoxy-substituted alkene (eq 3). The reaction has been used to prepare cycloheptadiene derivatives by cyclopropanation of dienes followed by [3,3]-sigmatropic rearrangement of the resulting divinylcyclopropane.

Vinyldiazomethane will readily undergo dipolar cycloaddition with electron-deficient alkenes to provide vinylpyrazolines.5 Vinylpyrazolines are less stable than typical alkylpyrazolines, and will undergo loss of N2 to provide the corresponding vinylcyclopropane with either thermal or photochemical activation. The reaction has been used to prepare vinylcyclopropyl steroid derivatives from D16-20-oxo-steroid derivatives (eq 4).2 Thermal extrusion of N2 provides the desired cyclopropane in 90% yield.

An interesting side reaction has been observed with alkenes that bear two electron-withdrawing substituents. These substrates do not provide the cyclopropane upon thermolysis, but give the product of insertion into C-H bonds on the carbon that is b to the carbonyl (eq 5).6 This is a general reaction which will work with other diazoalkanes.

Conjugated dienes will also undergo dipolar cycloaddition with vinyldiazomethane. The reaction occurs preferentially at the less substituted alkene, as predicted by FMO theory.7 The resulting pyrazolines undergo extrusion of N2 at rt or below to provide the corresponding divinylcyclopropyl derivatives. These compounds will then undergo [3,3]-sigmatropic rearrangement to provide cycloheptadiene derivatives. The cis-divinylcyclopropanes undergo sigmatropic rearrangement very rapidly, at times below rt. This has hindered attempts to obtain kinetic data for these substrates. However, they can be synthesized by low temperature (-40 °C) photolysis of pyrazolines derived from vinyldiazomethane and conjugated dienes.8 The reaction has been used to synthesize the algae metabolite dictyopterene DŽ via a vinylcyclopropyl derivative (eq 6).9

Allylation of Heteroatoms.

Vinyldiazomethane can be used to convert carboxylic acids to the corresponding allyl carboxylate.1c,3 However, the reaction has not been widely utilized. An interesting example of the allylation of an alcohol has been reported.10 Treatment of the vicinal steroidal diol shown in eq 7 with boric oxide provides the corresponding borate ester. Treatment of this compound with vinyldiazomethane provides the monoallyl ether with preferential reaction at the less hindered oxygen. Presumably, the reaction proceeds by protonation of the vinyldiazomethane by the borate ester to provide an allyldiazonium species which undergoes nucleophilic attack by oxygen.


1. (a) De Meijere, A.; Schulz, T-J.; Kostikov, R. R.; Graupner, F.; Murr, T.; Bielfeldt, T. S 1991, 547. (b) Hooz, J.; Kono, H.; OPP 1971, 3, 47. (c) Brewbaker, J. L.; Hart, H. JACS 1969, 91, 711.
2. Bladon, P.; Rae, D. R.; Tait, A. D. JCS(P1) 1974, 1468
3. Salomon, R. G.; Salomon, M. F.; Heyne, T. R. JOC 1975, 40, 756. See also Ref. 1c.
4. De Meijere, A.; Schulz, T-J.; Kostikov, R. R.; Graupner, F.; Murr, T.; Biefeldt, T. S 1991, 547.
5. Tabushi, I.; Takagi, K.; Okano, M.; Oda, R. T 1967, 23, 2621.
6. Dean, F. M.; Clinging, R. JCS(C) 1971, 3668.
7. Houk, K. N.; Sims, J.; Duke, R. E.; Strozier, R. W.; Georgie, J. K. JACS 1973, 95, 7287. Houk, K. N.; Sims, J.; Watts, C. R.; Luskus, L. J. JACS 1973, 95, 7301.
8. Schneider, M. P.; Rau, A. JACS 1979, 101, 4426.
9. Schneider, M. P.; Goldbach, M. JACS 1980, 102, 6114.
10. Cimarusti, C. M.; Grabowich, P.; Varma, R. V.; Chao, S. T.; Levine, S. D.; Weisborn, F. L. JOC 1977, 42, 3035.

Tarek Sammakia

University of Colorado, Boulder, CO, USA



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